1. Tracked Bipolar Stimulator
Greg Wempe
Advised by:
Dr. Robert L. Galloway, Ph.D.
Mr. Steven L. Hartmann
Final Presentation March 23, 2001

2. Project Background
Mapping of points on/in the brain is necessary in most surgical cases
Current pre-operative methodology limited
Stereotactic frames (top)
Current real-time methodology limited
Articulated arm (top/bottom)
“Post-It” notes
Three-dimensional tracking techniques are currently available and readily applicable

3. Tracking Stimulator Position and Spatial Orientation
24 infrared light emitting diodes (IREDs) which fire in time sequence spiral around the handle of the probe.
The sensor unit, the Optotrak, returns the position for each IRED that it can “see” every 300 microseconds.
The probe can be calibrated by creating a reference file, known as a rigid body file, containing the locations of each of the IREDs and the endpoint of the probe in a reference coordinate system.

4. Tracking Stimulator Position and Spatial Orientation
The location of the probe tip is then passed through a transformation matrix that calculates its position in sensor space.
The probe’s position is lastly mapped into the space defined by a small, stationary reference emitter with six IREDs. This allows the position of the sensor unit to drop out of the equations, and one gains the ability to move this large, cumbersome device without worry during use.

5. Target Problems
Inaccuracies in calibration caused by the lack of rigidity in stimulator leads
Inaccuracies in calibration caused by offset characteristic of stimulator carriage
Inaccuracies in calibration caused by inability to properly rotate bipolar system about a single point

6. Project Definition Design a sheath and carriage system that will
integrate into the present software package
and allow for the tracking and marking of
desired points. Additional software coding
may be required for proper incorporation.

7. Initial probe handle and carriage with ablator attachment.
Current Status
New registration software integrated.
Stimulator lead sheath is complete.
Rigid-body files (calibration) have been compiled.
Initial probe handle and carriage with ablator attachment.
Stimulator carriage connection to IRED probe is being machined.
Roll black-out isolated and eliminated.
Power source connectors must be converted for use on updated source.

8. Calibration Improvement
The probe’s dimensions were measured and used to design a sheath made from Delran. The sheath was flared to insure a secure fit against the stimulator lead cap and narrowed to provide necessary line-of-sight. The carriage will be cast from aluminum or steel.

9. Calibration Improvements
OPTOTRAK system provides 0.3mm accuracy to marker.
Iterative rigid-body calibration process insures 3D RMS error of 0.5mm.
Average largest single-marker error without sheath: ± 0.695mm.
Average largest single-marker error with sheath: ± 0.577mm.

10. The Optotrak 3220 Localizing Planes
Key Questions
Device linearity and effects on roll
Blackout orientation
Testing processes
Accuracy determination
The Optotrak 3220 Localizing Planes

11. Future Plans
Possible incorporation of labeling algorithm into registration
TREFRE analysis for sheath accuracy.
Rotation piece for use with 3mm ball.

12. Future Plans